1. Field of Invention
The present invention relates to a removable system that allows altering or tuning of the harmonic vibration pattern of a wide variety of firearm barrels which imparts an improvement to the accuracy of a firearm such equipped with no modification or alteration to the barrel.
2. Background and Description of Prior Art
Upon discharge, a firearm barrel begins a pattern of harmonic vibrations moving from chamber to muzzle and back. This vibration pattern is affected by the volume of the powder charge, the weight of the bullet, the design of the bullet shape, the seating depth of the bullet in relation to the bore, the rifling twist, the diameter of the barrel and the way in which the action and barrel are mounted to the stock of the firearm.
Each new combination of elements, such as changing from one brand of ammunition to another or changing bullet weight or bullet style will impart a new vibration pattern to the barrel. With each new combination the accuracy of the firearm can be affected. The normal shape of an impact pattern on a downrange target shows that the actual vibration pattern of the firearm muzzle is circular in nature around the axis of the bore. This circular vibration is caused by the spin imparted to the bullet by the spiral rifling in the bore. Additional vibrations are imparted by the sound created by the discharge of the propellant as well. This vibration pattern is present along the entire length of the barrel and moves in a wave motion along the axis of the bore in a series of vibration patterns. These patterns move first toward the muzzle along the barrel and then away from the muzzle, thus creating a harmonic effect not unlike a tuning fork.
Upon firing, if the bullet departs the muzzle at the greatest point of circular deflection in the harmonic vibration pattern the size of the impact pattern will be larger than if the bullet were to depart while the muzzle is at it's smallest circular deflection. Firearms designed for target shooting are normally equipped with a very heavy barrel of large diameter to minimize the vibration pattern and impart greater accuracy. Hunting firearms are designed with smaller diameter light weight barrels to provide greater portability and are therefore less likely to be accurate with all types of ammunition due to varying vibration patterns.
To a lesser extent, the design of the crown of the muzzle or what is actually beyond the end of the bore can affect accuracy as well. This is known as muzzle dynamics and deals with the action of expanding gases on the base of the bullet once it has departed the bore.
The harmonic vibration characteristics of a barrel can be altered by changing ammunition, changing the length of the barrel, changing the point at which a barrel contacts the forestock of the firearm or by changing the diameter or mass of the barrel.
Previously the reduction or control of barrel vibration has been approached in numerous ways. A Ballistic Optimizing System for Rifles (BOSS) patented by Rose of South Weber, Utah, U.S. Pat. No. 5,279,200 utilizes a permanently attached tube with vents or ports that can be adjusted to tune the vibration pattern of the barrel used in conjunction with a flexible barrel and action bedding compound where these contact the stock of the firearm. Unfortunately, this device is available only by purchasing a Browning or Winchester rifle equipped with the system. The most obvious drawback to this device is that it affords no improvement to a shooter's current firearm. If it were available, it would require permanent alteration of the barrel of the gun, another drawback that affects future value of a gun. Contrary to the patent claims, the BOSS also increases muzzle blast noise, it deflects propellant gas rearward with it's series of ports and even warns of the noise increase in advertising literature covering the BOSS system. Such additional noise can create a hazard for the shooter and any nearby observers. Another drawback to the BOSS is increased overall length since it is mounted such that it extends beyond the end of the muzzle. Since the BOSS is a permanent attachment, it cannot be removed and mounted on another gun. Were the BOSS available as an aftermarket product, it would require gunsmith installation and permanent modification to the barrel as well as permanent modification of the gunstock in applying the required flexible bedding compound. The BOSS system also has an effect on the muzzle dynamics of the gun that change with each new adjustment of the device.
A follow-up device similar to the BOSS U.S. Pat. No. 5,509,345 by Cyktich of Everett, Wash. also requires mounting a device substantially beyond the end of the muzzle. This device also has porting and was more or less permanently mounted onto the barrel of the gun with a type of heat shrink material. Drawbacks include increase in muzzle blast, it is not transportable from gun to gun, it requires a custom sized mounting device for each barrel, and an increase in overall length of a gun so equipped.
A Rifle Control Tube as patented by Shapel of Boise, Id. U.S. Pat. No. 2,796,005 utilized a combination of weight for dampening effect coupled with a system of vents to deflect propellant gases upward to reduce muzzle flip and recoil. The drawback to this system is the permanent modification necessary to the barrel of the gun, namely threading the muzzle for mounting. In addition, the venting system creates an increase in noise due to the deflection of muzzle blast. The system had no means of actually changing or tuning the vibration pattern to impart better accuracy with different types of ammunition. A further drawback to this type of system is the change in muzzle dynamics whereby the bullet departing the bore can be affected by deflected propellant gases. Another drawback is the additional length added to the barrel which makes gun handling more difficult. This device cannot be removed from one gun and placed on another without permanent barrel modification. This device could not be installed by an untrained shooter, and requires a professional to modify the firearm and mount the device.
Other means of dampening barrel vibration have been used. U.S. Pat. No. 4,726,280 by Frye relates to a means of mounting a muzzle member by threading the end of the barrel. This muzzle member could add sufficient weight to dampen or alter the vibration of the barrel, however, a permanent modification to the gun barrel is required. A further drawback is the additional length added to the gun. In addition, this device can adversely affect the muzzle dynamics of a firearm so equipped. This device also lacks the ability to be adjusted to tune the vibration pattern of the barrel for best accuracy.
Other muzzle "Brakes" have been utilized to lessen the recoil of a firearm by venting propellant gases in an attempt to offset rearward movement at discharge. These devices all require permanent modification of the gun barrel and cannot be attached by the average shooter. While most of these devices can add some weight to the end of the barrel, they all lack the ability to be adjusted or tuned for optimum accuracy. In many instances, barrels that have been modified and a muzzle brake added no longer shoot as accurately as before. All these devices tend to increase muzzle blast by deflecting propellant gases rearward toward the shooter.
A more recent development in an attempt to alter barrel vibration without adding significant weight was developed by Christianson Arms of Fayette, Utah (patent pending). This approach encases the entire barrel with a carbon fiber sleeve that adds stiffness to reduce barrel vibration. This design effectively creates a heavy barrel characteristic without the associated weight of a larger diameter barrel. The drawback to this system is high cost of a complete rifle. If the system were available as an aftermarket modification it would require barrel replacement and as a further drawback this barrel has no capability of adjusting or tuning for different types of ammunition because even heavy barrels have a certain amount of vibration to contend with.
U.S. Pat. No. 5,423,145, by Nasset of Aumsville, Oreg. is a device that tunes barrel vibrations by altering the contact point of the barrel to the forestock. This effectively changes the length of the vibration pattern from contact point to muzzle thus changing barrel harmonics. This system requires permanent modification of the gunstock which can affect future value. Another drawback is the device cannot be moved from gun to gun. Also, any barrel contact by the stock can affect point of impact if the stock gets wet. Wood stocks can swell and warp, fiberglass or composite stocks are stable in all conditions, but any moisture between the barrel and the contact point will affect the point of impact due to hydraulic effect. This device is also best installed by a competent gunsmith since a good deal of stock material must be removed from the barrel channel for installation and the barrel contact must be accurately centered below the barrel with a certain amount of pressure on the contact point.
Another approach to barrel vibration is addressed by American Safe Arms, Inc. as described in the January 1997 issue of Shooting Sports Retailer. This method is a complete redesign of the entire gun barrel. It has an inner barrel encased by an outer sleeve or barrel with a device at the muzzle that keeps the inner barrel stationary. The inner barrel is ported to direct propellant gases out and back inside the inner sleeve. This design lowers noise and reduces recoil at the same time. While a unique approach to the problem, the system is not something that a shooter can install themselves on their existing firearm. Another drawback is the lack of tuning capability within the system. This system obviously has no flexibility to move from gun to gun.
Another approach is an embodiment of the present invention as produced by Bill Shaw of Austin, Tex. in February of 1997. This proof of concept prototype was constructed for me by Mr. Shaw from my original drawings but he modified the design considerably. Mr. Shaw used a custom designed insert that was press fit onto the barrel and externally threaded to accept a tuning device of a nominal weight. The drawback to this design was the need for custom sized inserts for each different size barrel and no indexing capability for adjustments to the location of the tuning device. A further drawback was the lack of transportability between guns because a custom sized insert would be required for each.
In addition to these systems mentioned, the search for accuracy improving products has run to other types of devices such as improved bench rest devices, improved stock mounting systems, improved stock materials that are more stable under all conditions, interchangeable barrel weights of different sizes to dampen vibration, and custom tailored ammunition to match each gun specifically. All lack the ability to tune barrel vibrations with the same device and the ability to transport the device from gun to gun without custom modifications.